With some anecdotal evidence: my nephews autism (two nephews) have been improved (the symptoms lessened) by putting them on something called the "GAPS diet" for the past few years, moving them from pretty much being locked in a world of their own to interacting playfully with each other and making eye contact with trusted adults.

Of course, this is not a scientific study, and there may have been other influences in their improvement. But a definite improvement has been made.